If the primary winding is assembled to provide 30VA from a 230Vac supply then simply powering half the winding from 115Vac will reduce the transformer to 15VA.
You must ask the manufacturer what the VA rating is for a 115Vac supply.
The screen should be connected to the main electrostatic screen enclosing the whole amplifier. Not grounded.
The main screen is the metal Chassis
You must ask the manufacturer what the VA rating is for a 115Vac supply.
The screen should be connected to the main electrostatic screen enclosing the whole amplifier. Not grounded.
The main screen is the metal Chassis
The transformer is made in China, so anything is possible. It might not be genuine 30VA even when the full primary is used.
As I said, you ground the screen. The red lead must be isolated. That means either cut it off short and ensure that no wire pokes out (put a blob of glue on the end, or use insulating tape), or solder it to a spare isolated tag. In use it will have 230V on it as the primary will act as an autotransfomer. Be careful! The sort of questions you are asking make me concerned for your safety. Maybe you are not yet ready to be making mains PSUs?
As I said, you ground the screen. The red lead must be isolated. That means either cut it off short and ensure that no wire pokes out (put a blob of glue on the end, or use insulating tape), or solder it to a spare isolated tag. In use it will have 230V on it as the primary will act as an autotransfomer. Be careful! The sort of questions you are asking make me concerned for your safety. Maybe you are not yet ready to be making mains PSUs?
No worries DF. I do appreciate your concern though.
I'm probably overly cautious when dealing with mains and other potentially dangerous voltage levels. I'm just use to dealing with or seeing the winding diagram usually associated with a transformer. I don't like guessing! I would have figured it out using my VOM. It's been decades since my electronics training, so a few things are rusty. I'm not really making a PSU. Just hooking it up to a DAC PCB that's already designed and has dual, full-bridge rectifiers, filter caps and regulators onboard.
So.... should the SCN lead be grounded to my metal case or not? Thanks guys.
Andrew - you're killing me. My chassis will be grounded (earth ground as per just about everything I've read), and there will no other internal chassis. Just my aluminum enclosure. What am I not getting?!
One more question DF.... Should the PCB ground plane be connected to 'mains' (or earth) ground at some common point, or is it floating within the enclosure?
Thanks DF. I am doing some research and I offer this summary article by Dave Davenport of Raleigh Audio that I found helpful. My basic assumptions about audio grounding remain sound, it's just with DACs and other digital circuits I intend to build add a little different twist that must be dealt with. Also discussions about balanced and unbalanced inputs further confuses the issue.
Stop calling everthing "ground".
The third wire system is Protective Earth (PE), here in the UK we often shorten this to "Earth".
That is very different from the concept of audio ground.
Connect PE to the chassis - permanently.
Now connect the transformer screen to chassis, not to audio ground.
The third wire system is Protective Earth (PE), here in the UK we often shorten this to "Earth".
That is very different from the concept of audio ground.
Connect PE to the chassis - permanently.
Now connect the transformer screen to chassis, not to audio ground.
If everyone calls everything ground, without qualification, then everyone could potentially wire everything up incorrectly.
We need qualification !
We cannot rely on "ground" to specify a particular item.
Especially since the USA usage of ground applies to everything.
Being a newbie/beginner, or whatever, does not change the rules on ambiguity.
We need qualification !
We cannot rely on "ground" to specify a particular item.
Especially since the USA usage of ground applies to everything.
Being a newbie/beginner, or whatever, does not change the rules on ambiguity.
Andrew/DF,
My apologizes if I've made things more confusing. Since the internet is global, distinction needs to be made on occasion. Here in the US we NEVER use 'mains' either, but I get it and understand it relative to it's usage here.
To my point, I been very explicit with my use of ground. I'm just trying to get a better understanding of what is best practice when tying them together inside the chassis, since that's what ultimately happens at some point (pun intended).
Earth Ground is just that - the green wire from the wall outlet in the US. It's where it is tied to the earth - a copper rod 3' in the ground. This is also the enclosure or chassis ground. Maybe you would prefer to call it safety (Protective) ground. Earth ground has been around a long time here and so yes, it's ingrained in our technological vocabulary.
Signal Ground - the other half of the audio circuit relative to it's I/O. The ground plane of the audio PCB.
Those are the only two grounds I've been referring to. If I'm all wrong, then I suggest someone post a link to a good refresher document from a qualified individual. There have been some direct, contradictory statements made about the different grounds on this forum board. I'm just trying to find the clarity. And if there are 'other' grounds I should be concerned with please help enlighten me.
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The transformer screen and the chassis/case should be connected to earth ground/safety ground/protective earth. The chassis connection should be done in such a way that it is very unlikely to break. e.g. use shakeproof washers
The signal ground should have one and only one direct connection to safety ground, somewhere in your system. Elsewhere, it can have an indirect connection via a big low value resistor or a shorted rectifier bridge. Details are available in a number of places.
The signal ground should have one and only one direct connection to safety ground, somewhere in your system. Elsewhere, it can have an indirect connection via a big low value resistor or a shorted rectifier bridge. Details are available in a number of places.
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